Photographic emulsions



Patented Aug. '23, 1938 UNITED STATES rnorocaarnro EMULSIONS Samuel E. Sheppard and Robert C. Houck,

Rochester, N. Y., assignors, by meane assignments, to Eastman Kodak Company, Jersey City, N. J., a corporation oi New Jersey No'Drawing. Application April 16, 1936, 1 Serial No. 74,817

11 Claims.

This invention relates to photographic emulsions and particularly to photographic emulsions in which a cellulosic compound is used as the protective colloid for the light-sensitive salt.

a Photographic emulsions are customarily made by dispersing a silver halide in a solution of a protective colloid, such as gelatin. It has been proposed to substitute for the gelatin used to disperse the light-sensitive salt, other materials,

such as collodion, regenerated cellulose and water-insoluble cellulose esters, such as cellulose acetate. An example of the latter type of photographlc emulsion is disclosed in the U. S. Patent to Eichengrun No. 752,388, granted February ll 16, 1904. Such emulsions have not been satisfactory for various reasons, among which are the difllculty of manufacture and the low general sensitivity of the emulsions obtained, and therefore they have not come into general use.

In U. S. application Serial No. 74,814, filed April 16, 1936 Staud and Connelly have described photographic emulsions made by dispersing a silver halide in gelatin, then substituting for part or all of the gelatin, a water-soluble salt 2 or ester of an acid polycarboxylic acid ester of cellulose, or a hydroxymonocarboxylic acid ester of cellulose.'

We have found that photographic emulsions may be made by dispersing a silver halide in a 3 solution of a water-soluble or substantially water-soluble derivative of a carboxylic acid ester of cellulose, for example, alkali metal and other water-soluble metal salts of polycarboxylic acid esters of cellulose, and hydroxymonocarboxylic acid esters of cellulose.

In making an emulsion according to our invention a water solution of a substantially watersoluble salt f a carboxylic acid ester of cellulose is first made up. These compounds include polycarboxylic acid esters of cellulose, such as cellulose acid phthalate, cellulose acid succinate and cellulose citrate; mixed esters containing a polycarboxylic acid radical, such as cellulose acetate phthalate; and water solublesalts of these compounds, such as cellulose potassium phthalate, and cellulose acetate potassium phthalate. These compounds and a method of preparing them are described in Malm and Waring U. S. Patent No. 2,093,462, granted September 21, 1937. The general method of producing them is to treat a cellulosic-material, such as cellulose or cellulose acetate with a polycarboxylic acid anhydride, such as phthalic anhydride, in the presence of an organic base, such as pyridine,

5 quinoline, or the like. The resulting product in esters of cellulose.

that case is then washed with dilute acid to remove substantially all of the pyridine or other base and to give a polycarboxylic acid ester of cellulose in which each of the polycarboxylic acid radicals presents a free, unesterified carboxylic group. This group may then be treated with an alkali metal hydroxide to produce an alkali metal salt.

Another type of polycarboxylic acid ester which may be used according to our invention is that formed by reacting an ethanolamine with an acid polycarboxylic acid ester of cellulose. Compounds of this type are cellulose phthalate tri-' ethanolamine salt, the production of which is described in FordyceU. S. Patent No. 1,969,741, August 14, 1934. e

Still another type of compound, the alka metal salts of which may be used according to our invention, is the group of heterogeneously linked dicarboxylic acid esters of cellulose, such as cellulose dilactate, cellulose diglycollate, cellulose acetate diglycollate, etc. These compounds are described in Malm and Fordyce U. S. Patent No. 2,024,238, December 17, 1935.

We may also use as protective colloids for the sensitive silver salt, hydroxy-monocarboxylic acid Compounds of this class are cellulose acetate glycollate, cellulose acetate hydracrylate, cellulose acetate lactate, and cellulose acetate propionate glycollate. Compounds of this classare described in Staud and Webber U. S. Patent No. 1,957,856, May 4, 1934.

Any water-soluble alkali metal salts of these compounds may be used although we have found the potassium andammonium salts particularly useful. The alkaline earth metal salts, such as calcium or any of the metals which form insoluble salts of the acid esters of cellulose are unsuitable for the purposes of our invention. The water-solubilities of these cellulose compounds depend in large measure upon the ionization of the metalatom or other group attached to the free carboxyl of the polycarboxylic acid. The proportion of these solubilizing groups in the molecule is, therefore, of importance in determining the water-solubility of the cellulose compound used. v

To the water solution of the cellulose carboxylic acid ester there are added suitable amounts of salts which form a sensitive compound by double decomposition, for example, silver nitrate and an alkali metal halide, and a silver halide is thereby formed in the presence of the carboxylic acid ester. We have found that the silver halide formed in this way is not prepresence of exoesizfialide it may be ripened by digestion, althoug n this case a larger amount of the cellulose ester is required to keep it in suspension.

These suspensions and particularly the silver halide hydrosols as they exist before digestion as described above, can be rapidly and completely coagulated by the addition of a very small amount of a compound which furnishes in solution a polyvalent cation, such as aluminum chloride or aluminum sulfate. The coagulum formed in this way can be very rapidly washed free of excess salts, such as potassium nitrate and bromide or chloride without peptization or loss of silver halide. The silver halide can then be readily repeptized to a fine hydrosol on addition of a gelatin solution containing a small amount of 1 alkali metal citrate or tartrate or lactate, or other polybasic or hydroxy organic acid. This effect may be explained by the factthat these polybasic or hydroxy organic acids form complexes with the polyvalent cations, such as aluminum, thereby destroying their coagulating efiect upon the silver halide hydrosol in the presence of the cellulosic compound.

The following specific example illustrates one method of forming an emulsion according to our invention, it being understood that, this example is merely illustrative.

Example About 120 to 125 grams of potassium bromide are dissolved in a liter of water containing 5 to 7.5 grams of the potassium salt of cellulose acetate diphthalate. To this solution is added, with stirring, about 170 grams 'of silver nitrate dissolved in a small amount of water. A hydrosol of silver bromide is formed and this is coagulated by the addition of a few cubic centimeters of a 1/10 normal solution of aluminum chloride. The coagulum is washed by decantation with several changes of distilled water and is then repeptized in a 5 to 7% solution of gelatin containing 5 to 10 cc. of 1/10 normal sodium citrate. The volume of gelatin depends upon the ratio of silver halide to gelatin desired in the finished emulsion. The emulsion may be given a slight digestion to increase the sensitivity and is then ready to coat on the support.

If a ripening or re-crystallization of the first suspension is desired in the above example, the digestion may be carried out with the original suspension but with high concentrations of the silver compound, before coagulation and removal of free halide.

The emulsions produced according to our invention may be used as print-out emulsions, that is, to form an image directly by exposure to light, or as developing emulsions. In general, these emulsions when used as print-out emulsions show a lower sensitivity than equivalent emulsions in which gelatin is used as the protective colloid. However, the sensitivity of the emulsions formed in the cellulose compounds may be raised by addition of halogen acceptors, such as sodium nitrite, acetone semi-carbazide, silver citrate and the like. 7

After coating, emulsion layers formed with these cellulosic compounds may be insolubilized by treatment with a dilute acid, such as hydrochloric acid, or dilute aluminumsalt solutions, washed free of the excess coagulant, and dried.

Numerous advantages are'obtained by the use cipitated from solution but remains suspended in of emulsions formed in cellulosic compounds ac-. the form of a fine colloidal dispersion. In thHording to our invention, with or without the\ presence of small amounts of gelatin. Layers obtained in this way are suitable for developing out in acid developers which are highly resistant to high temperatures, thereby making these emulsions desirable for use in tropical climates. The images produced in these, emulsions exhibit a very fine grain since after-ripening and coarsening of the grain can be prevented by the removal of excess halide.

It is to be understood that we are not limited to the use of the compounds or to the methods of procedure described above but that our invention is limited only by the scope of the appended claims.

What we claim is:

1. The method of making a sensitive photographic emulsion which comprises precipitating a silver halide in an aqueous solution of a sub stantially water-soluble cellulose compound selected from the group consisting of cellulose hydroxy-monocarboxylic acid esters and alkali metal salts of cellulose polycarboxylic acid esters.

2. The method of making a sensitive photographic emulsion which comprises precipitating a silver halide in an aqueous solution of a substantially water-soluble hydroxymonocarboxylic acid ester of cellulose.

3. The method of making a sensitive photographic emulsion which comprises precipitating a silver halide in an aqueous solution of a water soluble alkali metal salt of a polycarboxylic acid ester of cellulose.

4. The method of making a sensitive photographic emulsion which comprises precipitating a silver halide in an aqueous solution of a substantially water-soluble alkali metal salt of a polycarboxylic acid ester of cellulose, coagulating the silver halide and cellulose ester with a compound yielding in solution a polyvalent cation, washing the emulsion to remove excess salts, repeptizing the silver halide, and ripening the resulting emulsion.

- 5. The method of making a sensitive photographic emulsion which comprises precipitating a silver halide in an aqueous solution of a substantially water-soluble alkali metal salt of a polycarboxylic acid ester of cellulose, coagulating the silver halide and cellulose ester with a compound yielding in solution a polyvalent cation, washing the emulsion to remove excess salts, repeptizing the silver halide in admixture with gelatin, and ripening the resulting emulsion.

6. In the method of making a sensitive photographic emulsion by precipitating a silver halide in an aqueous solution of a substantially watersoluble cellulose compound selected from the group consisting of cellulose hydroxy-monocarboxylic acid esters and alkali metal saltsof cellulose polycarboxylic acid esters, the step which comprises coagulating the precipitated silver halide and the cellulose compound with a compound yielding in solution a polyvalent cation.

7. In the method of making a sensitive photographic emulsion by precipitating a silver halide graphic emulsion which comprises precipitating a silver halide i'n an aqueous solution of an alkali metal salt of a polycarboxylic acid ester of cellulose, coagulating'the-silver halide and the cellu lose ester with an aluminum salt, washing the emulsion to remove excess salts, and repeptizing the silver halide in admixture with gelatin with an alkali metal salt of an aliphatic carboxylic acid having not more than three carboxyl groups.

9. The method of making a sensitive photographic emulsion which comprises precipitating a silver halide in an aqueous solution of an alkali metal salt of a polycarboxylic acid ester of cellulose, coagulating the silver halide and the cellulose ester with an aluminum salt, washing the emulsionto remove excess salts, and repeptizing the silver halide with an alkali metal salt of lactic acid in admixture with gelatin.

10. In the method of making a sensitive photographic emulsion by precipitating a silver halide in an aqueoussolution of a water-soluble organic acid ester of cellulose and coagulating the precipitated silver halide and the cellulose ester, the step of repeptizing the coagulated silver halide and cellulose ester in the admixture with gelatin with an alkali metal salt of a polycarboxylic acid having not more than three carboxyl groups.

11. In the method of making a sensitive photographic emulsion by precipitating a silver halide in an aqueous solution of a water-soluble organic acid ester of cellulose and coagulating the precipitated silver halide and the cellulose ester, the step of repeptizing the coagulated silver halide and cellulose ester in admixture with gelatin with an alkali metal salt of lactic acid.

SAMUEL E. SHEPPARD. ROBERT C. HOUCK. 

